Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method of operating a terminal in a carrier aggregation system, and an apparatus using the method.
Related Art
A wireless communication system may use a hybrid automatic repeat request (HARQ). The HARQ is a scheme in which a transmitter transmits data and receives acknowledgement (ACK)/not-acknowledgement (NACK) which is reception confirmation information with respect to the data, and transmits new data or retransmits the transmitted data according to the ACK/NACK.
3rd generation partnership project (3GPP) long term evolution (LTE)/long term evolution-advanced (LTE-A) may transmit the ACK/NACK through a physical uplink control channel (PUCCH) which is an uplink control channel. When the ACK/NACK is transmitted through the PUCCH, a resource in the PUCCH (i.e., a PUCCH resource) may be implicitly or explicitly determined. For example, the PUCCH resource may be determined based on a resource occupied by a physical downlink shared channel (PDSCH) which is a target of the ACK/NACK response or a control channel for scheduling data (e.g., a transmission block or a code-word). Such a PUCCH resource is called an implicit PUCCH resource. The control channel may be a physical downlink control channel (PDCCH). On the other hand, in a case where one or a plurality of resources are explicitly indicated by a higher-layer signal, and at least one of the resources is used, such a resource is called an explicit PUCCH resource.
Meanwhile, it is considered to use an additional control channel in the wireless communication system in addition to the existing PDCCH. The additional control channel is called an enhanced PDCCH (E-PDCCH). The PDCCH is distinguished from a PDSCH which is a data channel in a time domain. However, the E-PDCCH may exist in the same time domain as the PDSCH and may be distinguished only in a frequency domain. That is, the E-PDCCH may be included in a region in which the PDSCH is allocated.
User equipments (UEs) may receive data scheduled through the PDCCH or the E-PDCCH, and may transmit ACK/NACK for the data. When a PUCCH resource is implicitly used in ACK/NACK transmission of the UEs, a collision situation may occasionally occur in which the same implicit PUCCH resource is allocated between different UEs. There is a need to solve such a problem.
In addition, regarding the conventional explicit PUCCH resource, one of a plurality of resources configured by a higher layer is indicated by using a transmission power control (TPC) field included in downlink control information (DCI) transmitted through the PDCCH. The TPC field is originally used to control uplink transmission power, and is alternatively used to indicate the explicit PUCCH resource.
In case of a UE for which data is scheduled through the E-PDCCH, how to allocate and operate a PUCCH resource is a matter to be considered.